KR101295882B1 - Liquid crystal display and local dimming control method of thereof - Google Patents

Liquid crystal display and local dimming control method of thereof Download PDF

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KR101295882B1
KR101295882B1 KR1020090116808A KR20090116808A KR101295882B1 KR 101295882 B1 KR101295882 B1 KR 101295882B1 KR 1020090116808 A KR1020090116808 A KR 1020090116808A KR 20090116808 A KR20090116808 A KR 20090116808A KR 101295882 B1 KR101295882 B1 KR 101295882B1
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value
dimming
block
light
pixel
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KR1020090116808A
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Korean (ko)
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KR20110060268A (en
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조병철
권경준
안희원
박창균
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엘지디스플레이 주식회사
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    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3406Control of illumination source
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/3406Control of illumination source
    • G09G3/342Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
    • G09G3/3426Control of illumination source using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines the different display panel areas being distributed in two dimensions, e.g. matrix
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0233Improving the luminance or brightness uniformity across the screen
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/06Adjustment of display parameters
    • G09G2320/0626Adjustment of display parameters for control of overall brightness
    • G09G2320/064Adjustment of display parameters for control of overall brightness by time modulation of the brightness of the illumination source
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/06Adjustment of display parameters
    • G09G2320/0626Adjustment of display parameters for control of overall brightness
    • G09G2320/0646Modulation of illumination source brightness and image signal correlated to each other
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00Aspects of the architecture of display systems
    • G09G2360/16Calculation or use of calculated indices related to luminance levels in display data

Abstract

The present invention relates to a liquid crystal display device capable of improving the contrast ratio of a display image.
The liquid crystal display device comprises a liquid crystal display panel; A backlight unit including a plurality of light sources for irradiating light to a rear surface of the liquid crystal display panel; A backlight driving circuit for driving the light sources in predetermined block units based on the dimming value for each block; And a local dimming control circuit for calculating a pixel gain value for compensating for the decrease in luminance due to the dimming value for each block, and correcting the pixel gain value according to the degree of gradation of each block.

Description

Liquid crystal display and local dimming control method {LIQUID CRYSTAL DISPLAY AND LOCAL DIMMING CONTROL METHOD OF THEREOF}

The present invention relates to a liquid crystal display device capable of improving the contrast ratio of a display image.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. This liquid crystal display device is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and an indoor / outdoor advertisement display device. The liquid crystal display displays an image by using a thin film transistor (TFT) as a switching element. The transmissive liquid crystal display device, which occupies most of the liquid crystal display device, displays an image by controlling an electric field applied to the liquid crystal layer to modulate the light incident from the backlight unit.

The image quality of the liquid crystal display device depends on the contrast characteristics. Only the method of modulating the light transmittance of the liquid crystal layer by controlling the data voltage applied to the liquid crystal layer has a limitation in improving this contrast characteristic. In order to improve the contrast characteristic, a backlight dimming method of adjusting the brightness of the backlight unit according to an image has been proposed. The backlight dimming method includes a global dimming method for adjusting the brightness of the entire display surface and a local dimming method for locally adjusting the brightness of the display surface. The global dimming method may improve dynamic contrast measured between the previous frame and the next frame. The local dimming method can improve the static contrast which is difficult to improve by the global dimming method by locally controlling the brightness of the display surface within one frame period.

The local dimming method divides the backlight into a plurality of blocks and adjusts the dimming value for each block to increase the backlight luminance of the bright block while reducing the backlight luminance of the dark block. In local dimming, the light sources of the backlight are turned on in blocks, that is, partially. Therefore, the backlight luminance when local dimming is applied is smaller than the backlight luminance with which all the light sources are turned on without local dimming. Insufficient luminance due to local dimming can be compensated through modulation of the pixel data. Compensation of the pixel data is performed based on the pixel gain value according to the light amount analysis result of the backlight for each block.

The pixel gain value is a dimming value for each block. The data gain must be compensated to the luminance value by the total amount of light reaching the pixel at the time of local dimming (the amount of light at the time of dimming) to reach the pixel at non-local dimming. It is determined on the basis of whether the luminance value is determined by the total amount of light (the amount of light at the time of nondimming). The pixel gain value is calculated by the ratio of the amount of light at the time of non-dimming and the amount of light at the time of dimming. The pixel gain value of the pixel increases as the amount of light at dimming is smaller than the amount of light at non-dimming. As the pixel gain value increases, the up modulation width of the data increases, and as a result, a gray level aggregation phenomenon in which high grays have the same brightness occurs. When the gradation of the tone is intensified, the image quality deteriorates. Therefore, there is a need for a method of controlling the pixel gain value according to the degree of gradation aggregation.

Accordingly, an object of the present invention is to provide a liquid crystal display device and a local dimming control method thereof in which image quality can be improved by correcting pixel gain values according to the degree of gradation in local dimming.

In order to achieve the above object, the liquid crystal display device according to an embodiment of the present invention comprises a liquid crystal display panel; A backlight unit including a plurality of light sources for irradiating light to a rear surface of the liquid crystal display panel; A backlight driving circuit for driving the light sources in predetermined block units based on the dimming value for each block; And a local dimming control circuit for calculating a pixel gain value for compensating for the decrease in luminance due to the dimming value for each block, and correcting the pixel gain value according to the degree of gradation of each block.

According to an exemplary embodiment of the present invention, a local dimming control method of a liquid crystal display device including a liquid crystal display panel and light sources irradiating light on a rear surface of the liquid crystal display panel may be configured in units of blocks based on dimming values of blocks. Driving (A); And calculating (B) a pixel gain value for compensating for a decrease in luminance due to the dimming value for each block, and correcting the pixel gain value according to the degree of gradation of each block.

In the liquid crystal display and the local dimming control method according to the present invention, the image quality is increased by automatically adjusting the pixel gain value by adjusting the amount of light at the time of non-dimming or the dimming value for each block according to the degree of gradation when local dimming is implemented. Can be improved.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 1 to 9.

1 shows a liquid crystal display according to an embodiment of the present invention.

1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a timing controller 11, a data driving circuit 12, a gate driving circuit 13, and a local dimming control circuit 14. ), A backlight driving circuit 15, and a backlight unit 16.

The liquid crystal display panel 10 includes two glass substrates and a liquid crystal layer formed therebetween. A plurality of data lines DL and a plurality of gate lines GL are intersected with each other on a lower glass substrate of the liquid crystal display panel 10. [ The liquid crystal cells Clc are arranged in a matrix form in the liquid crystal display panel 10 by the intersection structure of the data lines DL and the gate lines GL. Each of the liquid crystal cells Clc includes a TFT, a pixel electrode 1 connected to the TFT, and a storage capacitor Cst. On the upper glass substrate of the liquid crystal display panel 10, a black matrix, a color filter, a common electrode 2, and the like are formed. The common electrode 2 is formed on the upper glass substrate in a vertical electric field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode, and has an in plane switching (IPS) mode and a fringe field switching (FFS) mode. In the same horizontal electric field driving method, the pixel electrode 1 is formed on the lower glass substrate. The liquid crystal cells Clc include R liquid crystal cells for red display, G liquid crystal cells for green display, and B liquid crystal cells for blue display. The R liquid crystal cell, the G liquid crystal cell, and the B liquid crystal cell constitute one unit pixel. On the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, a polarizing plate is attached and an alignment film for forming a pre-tilt angle of the liquid crystal is formed on the inner surface in contact with the liquid crystal.

The timing controller 11 supplies digital video data RGB input from a system board on which an external video source is mounted, to the local dimming control circuit 14, and modulated data R modulated by the local dimming control circuit 14. 'G'B') is supplied to the data driving circuit 12. The timing controller 11 includes timing control signals for controlling the operation timing of the data driving circuit 12 and the gate driving circuit 13 based on the timing signals Vsync, Hsync, DE, and DCLK from the system board. DDC, GDC). The timing controller 11 inserts an interpolation frame between the frames of the input video signal input at a frame frequency of 60 Hz and multiplies the data timing control signal DDC and the gate timing control signal GDC to obtain 60 × N The operation of the data driving circuit 12 and the gate driving circuit 13 can be controlled with a frame frequency of Hz or more.

The data driver circuit 12 includes a plurality of data drive integrated circuits. The data drive integrated circuit stores a shift line for sampling a clock signal, a register for temporarily storing digital image data (RGB), and one line of data in response to a clock signal from the shift register, and stores the stored one line of data. A latch for outputting at the same time, a digital / analog converter for selecting a positive / negative gamma voltage under reference to a gamma reference voltage corresponding to a digital data value from the latch, and an analog converted by a positive / negative gamma voltage And a multiplexer for selecting a data line DL to which data is supplied, and an output buffer connected between the multiplexer and the data line DL. The data driving circuit 12 latches the modulated data R'G'B 'under the control of the timing controller 11 and outputs the latched modulated data R'G'B' to positive / negative polarity gamma compensation Voltage to the positive polarity / negative polarity analog data voltage, and supplies it to the data lines DL.

The gate driving circuit 13 includes a plurality of gate drive integrated circuits. The gate drive integrated circuit includes a shift register, a level shifter for converting an output signal of the shift register into a swing width suitable for driving a TFT of a liquid crystal cell, an output buffer, and the like. The gate driving circuit 13 sequentially outputs scan pulses (or gate pulses) to the gate lines GL under the control of the timing controller 11, thereby selecting a horizontal line to which a data voltage is applied.

The local dimming control circuit 14 analyzes the input data RGB to derive a representative value for each block, and according to the representative value for each block, the dimming value for each block for controlling the light sources of the backlight unit 16 in units of blocks. Is determined. After calculating a pixel gain value for compensating for the luminance deterioration due to the dimming value DIM for each block, the input data RGB is compensated based on the pixel gain value. The local dimming control circuit 14 analyzes the compensated data and calculates the degree of gradation of the gradation, and adjusts the amount of light at the time of non-dimming so that the prediction value for the gradation of the gradation converges to a predetermined target value, or the dimming value for each block ( DIM) (adjust the amount of light when dimming) to correct the pixel gain. The data compensated with the corrected pixel gain value is output as final modulation data R'G'B '.

The backlight driving circuit 15 blocks light sources of the backlight unit 16 by pulse width modulation (PWM) in which the duty ratio is changed according to the block-specific dimming value DIM input from the local dimming control circuit 14. Drive in units. The turn-on time of the light sources is controlled by the PWM duty ratio.

The backlight unit 16 includes a plurality of light sources and divides the surface light source irradiated to the liquid crystal display panel 10 into blocks in a matrix form. The backlight unit 16 may be implemented as either a direct type or an edge type. The direct-type backlight unit 16 has a structure in which a plurality of optical sheets and a diffusion plate are stacked under the liquid crystal display panel 10, and a plurality of light sources are disposed under the diffusion plate. The edge type backlight unit 16 has a structure in which a plurality of optical sheets and a light guide plate are stacked below a liquid crystal display panel 10 and a plurality of light sources are disposed on a side surface of the light guide plate. The light sources may be implemented as point light sources such as light emitting diodes (LEDs).

2 shows an example of the local dimming control circuit 14 that can correct the pixel gain value according to the degree of gradation. The local dimming control circuit 14 of FIG. 2 corrects the pixel gain value by adjusting the amount of light at the time of non-dimming according to the degree of gradation.

Referring to FIG. 2, the local dimming control circuit 14 includes an image analyzer 141, a dimming value determiner 142, a light amount deriving unit 143, a gain value calculating unit 144, and a data modulating unit 145. , A bitmap analysis unit 146, and a light amount adjusting unit 147.

The image analyzer 141 divides the input digital data RGB into virtual blocks BLK [1,1] to BLK [n, m, which are divided in a matrix form on the display screen of the liquid crystal display panel 10 as shown in FIG. ]) A representative value is obtained for each block by analyzing in units. The representative value for each block can be obtained by deriving a maximum gray value from among RGB values of pixels in each block and dividing the sum of the maximum values by the number of pixels included in the block.

The dimming value determiner 142 determines a dimming value DIM for each block by mapping a representative value for each block from the image analyzer 141 to a preset dimming curve. The dimming curve can be implemented as a look-up table. The dimming value per block DIM may be determined to be high in a block having a high representative value of data and low in a block having a low representative value.

The light amount deriving unit 143 calculates the amount of light reaching the pixel at the time of non-dimming (the amount of light at non-dimming) and the amount of light reaching the pixel at the time of local dimming at the dimming value per block (DIM). Derived pixel by pixel. The light amount during non-dimming indicates the total amount of light reaching the corresponding pixel when all the light sources of the backlight are turned on at a constant brightness. When dimming, the amount of light is analyzed with a size of P (block number) × P (block number) (P is an odd odd number of 3 or more) surrounding the block containing the pixel at the time of local dimming as shown in FIG. 4. It indicates the total amount of light reaching the pixel in the area. The amount of light upon dimming is determined by the block-specific dimming value DIM of the blocks in the analysis region.

The gain calculator 144 calculates a pixel gain value G for each pixel based on the amount of light at the time of non-dimming and the amount of light at the time of dimming from the light amount deriving unit 143. The gain value calculator 144 divides the amount of light at the time of non-dimming by the amount of light at the time of dimming, and calculates the pixel gain value G by performing a 1 / γ power exponential operation on the result.

The data modulator 145 compensates the input data RGB by modulating the data by multiplying the pixel gain value G from the gain value calculator 144 by the input data RGB.

The bitmap analyzer 146 analyzes the data of the compensated one frame in a bitmap manner to calculate the degree of gray level aggregation, and generates a prediction value for the degree of gray level aggregation. In the bitmap method, the maximum gray scale is sequentially scanned by scanning the compensation data for one frame while moving an analysis mask of size k (pixels) × k (pixels) (k is a positive integer) from side to side or up and down by one pixel interval. Is replaced with "1", and other grayscale pixel data is replaced with "0". The bitmap analyzer 146 counts the number of " 1s " to increase the predicted value of the gray level when the count value is large, and lowers the predicted value of the gray level by the count value. Here, the degree of gray level aggregation is larger when the predicted value is higher than when the predicted value is low.

The light amount controller 147 adjusts the amount of light at the time of non-dimming according to the predicted value from the bitmap analyzer 146 and feeds it back to the gain value calculator 144. If the predicted value is larger than the predetermined target value, the light amount adjusting unit 147 decreases the amount of light at the time of non-dimming. On the contrary, if the predicted value is smaller than the target value, the light amount adjusting unit 147 increases the amount of light at the time of non-dimming and converges the predicted value to the target value. The target value may be selected as an appropriate value to reduce the level of gradation while having a power consumption reduction effect. The gain value calculator 144 corrects the pixel gain value G so that the amount of light is adjusted during non-dimming, and supplies it to the data modulator 145. The data modulator 145 outputs the input data RGB multiplied by the pixel gain value G corrected so that the predicted value is equal to the target value, as the final modulation data R'G'B '.

The bitmap analyzer 146 and the light amount controller 147 may be integrated into the gain value corrector 148.

5 shows another example of the local dimming control circuit 14 that can correct the pixel gain value according to the degree of gradation. The local dimming control circuit 14 of FIG. 5 corrects the pixel gain value by adjusting the dimming value for each block (adjusting the amount of light when dimming) according to the degree of gradation.

Referring to FIG. 5, the local dimming control circuit 14 includes an image analyzer 241, a dimming value determiner 242, a light amount deriving unit 243, a gain value calculating unit 244, and a data modulating unit 245. , A bitmap analyzer 246, and a dimming value controller 247.

The image analyzer 241 divides the input digital data RGB into virtual blocks BLK [1,1] to BLK [n, m, which are divided in a matrix form on the display screen of the LCD panel 10 as shown in FIG. ]) A representative value is obtained for each block by analyzing in units. The representative value for each block can be obtained by deriving a maximum gray value from among RGB values of pixels in each block and dividing the sum of the maximum values by the number of pixels included in the block.

The dimming value determiner 242 determines the dimming value DIM for each block by mapping a representative value for each block from the image analyzer 241 to a preset dimming curve. The dimming curve can be implemented as a look-up table. The dimming value per block DIM may be determined to be high in a block having a high representative value of data and low in a block having a low representative value.

The light amount deriving unit 243 calculates the amount of light reaching the pixel at the time of non-dimming (the amount of light at non-dimming) and the amount of light reaching the pixel at the time of local dimming at the dimming value per block (DIM). Derived pixel by pixel. The light quantity at non-dimming indicates the total amount of light reaching the pixel when all the light sources of the backlight are turned on at a constant brightness (eg, the maximum brightness). When dimming, the amount of light is analyzed with a size of P (block number) × P (block number) (P is an odd odd number of 3 or more) surrounding the block containing the pixel at the time of local dimming as shown in FIG. 4. It indicates the total amount of light reaching the pixel in the area. The amount of light at the time of dimming may vary by the change of the block-specific dimming value (DIM) of the blocks in the analysis region.

The gain calculator 244 calculates a pixel gain value G for each pixel based on the amount of light at the time of non-dimming and the amount of light at the time of dimming from the light amount deriving unit 243. The gain value calculator 244 divides the amount of light at the time of non-dimming by the amount of light at the time of dimming, and calculates the pixel gain value G by performing a 1 / γ power exponential operation on the result.

The data modulator 245 compensates the input data RGB by modulating the data by multiplying the pixel gain value G from the gain value calculator 244 by the input data RGB.

The bitmap analyzer 246 analyzes the data of the compensated one frame by a bitmap method to calculate the degree of gray level aggregation, and generates a prediction value for the degree of gray level aggregation. In the bitmap method, the maximum gray scale is sequentially scanned by scanning the compensation data for one frame while moving an analysis mask of size k (pixels) × k (pixels) (k is a positive integer) from side to side or up and down by one pixel interval. Is replaced by "1", and other grayscale pixel data is replaced by "0". The bitmap analyzer 246 counts the number of " 1s " to increase the predicted value of the gray level when the count value is large, and decreases the predicted value of the gray level by the count value. Here, the degree of gray level aggregation is larger when the predicted value is higher than when the predicted value is low.

The dimming value adjusting unit 247 adjusts the dimming value DIM for each block according to the predicted value from the bitmap analyzer 246 and feeds it back to the light amount deriving unit 243. The dimming value adjusting unit 247 increases the dimming value (DIM) for each block by up-modulating the dimming curve as shown in FIG. 6 when the predicted value is larger than the predetermined target value, and conversely, dimming curve as shown in FIG. By down-modulating to reduce the dimming value (DIM) for each block, the predicted value is converged to the target value. The dimming value adjusting unit 247 outputs the dimming value DIM for each block when the predicted value converges to the target value as the final dimming value. The target value may be selected as an appropriate value to reduce the level of gradation while having a power consumption reduction effect. The light amount deriving unit 243 varies the amount of light when dimming in response to the adjusted dimming value DIM for each block. The gain value calculator 244 corrects the pixel gain value G and supplies it to the data modulator 245 as the amount of light varies during dimming. The data modulator 245 outputs the input data RGB multiplied by the pixel gain value G corrected so that the predicted value is equal to the target value, as the final modulation data R'G'B '.

The bitmap analyzer 246 and the light amount controller 247 may be integrated into the gain value corrector 248.

7 shows an example in which gradation aggregation is improved after application of the present invention.

Referring to FIG. 7, it can be easily seen that, when the present invention is applied, the gray level aggregation for the high gray area is improved as a whole compared to the conventional (before the application of the present invention), and the image quality is dramatically improved.

8 shows an example of a local dimming control method capable of correcting a pixel gain value according to the degree of gradation aggregation.

Referring to FIG. 8, in this local dimming control method, input data RGB is analyzed in virtual block units divided in matrix form on a display screen of a liquid crystal display panel to derive a representative value for each block (S11 and S12). The dimming value for each block is determined by mapping the representative value for each block to a preset dimming curve (S13).

This local dimming control method derives the amount of light at the time of non-dimming and the amount of light at the time of dimming. (S14) The amount of light at the time of non-dimming reaches the pixel when all the light sources of the backlight are turned on at a constant brightness during non-dimming. Directs the total amount of light. The amount of light when dimming is a dimming value for each block and has a size of P (block number) × P (block number) (P is an odd odd number of 3 or more) surrounding the block containing the pixel at the time of local dimming. It indicates the total amount of light reaching the pixel in the analysis area. The amount of light upon dimming is determined by the block-specific dimming values of the blocks in the analysis region.

The local dimming control method calculates a pixel gain value (G) for each pixel based on the amount of light at the time of non-dimming and the amount of light at the time of dimming. (S15) Then, the pixel gain value G is multiplied by the input data RGB to obtain data. The input data RGB is compensated by modulating (S16). The pixel gain value G may be obtained by dividing the amount of light at non-dimming by the amount of light at dimming, and performing a 1 / γ power exponent on the result. .

This local dimming control method analyzes the data of the compensated one frame by bitmap method, calculates the degree of gray level aggregation, and generates a predicted value for the degree of gray level aggregation (S17). × k (number of pixels) (k is a positive integer) Subsequently scanning the compensation data for one frame while moving the analysis mask of one pixel interval left and right or up and down, replacing the pixel data of maximum gradation with "1". Then, the other gray level pixel data is replaced with "0". This local dimming control method counts the number of " 1 " to increase the predicted value of the degree of gradation when the count value is large, and decreases the predicted value of the degree of gradation aggregation when the count value is small. Here, the degree of gray level aggregation is larger when the predicted value is higher than when the predicted value is low.

When the predicted value is larger than the predetermined target value (S18), the local dimming control method reduces the amount of light during non-dimming (S19), and feeds the result back to S15 to perform the processes S15 to S18 again. If the predicted value is smaller than the predetermined target value (S20), the amount of light is increased during non-dimming (S21), and the result is fed back to S15 to perform the processes S15 to S20 again. This local dimming control method corrects the pixel gain value (G) through the above feedback process and converges the predicted value to the target value. The target value may be selected as an appropriate value to reduce the level of gradation while having a power consumption reduction effect.

The local dimming control method compensates the input data RGB with the pixel gain value G corrected so that the predicted value is equal to the target value, and outputs the final modulation data R'G'B ', and the block determined in S13. The individual dimming value is output as the final dimming value (S22).

9 shows another example of a local dimming control method capable of correcting a pixel gain value according to the degree of gradation aggregation.

Referring to FIG. 9, in this local dimming control method, the representative data for each block is derived by analyzing the input data RGB in virtual block units divided in a matrix form on the display screen of the liquid crystal display panel (S111, S112). The dimming value for each block is determined by mapping the representative value for each block to a preset dimming curve (S113).

This local dimming control method derives the amount of light at the time of non-dimming and the amount of light at the time of dimming (S114). Directs the total amount of light. The amount of light when dimming is a dimming value for each block and has a size of P (block number) × P (block number) (P is an odd odd number of 3 or more) surrounding the block containing the pixel at the time of local dimming. It indicates the total amount of light reaching the pixel in the analysis area. The amount of light at the time of dimming may vary by the change of the block-specific dimming value (DIM) of the blocks in the analysis region.

This local dimming control method calculates a pixel gain value (G) for each pixel based on the amount of non-dimming light and the amount of dimming light (S115). The pixel gain value G is multiplied by the input data RGB to obtain data. The input data RGB is compensated by modulating (S116). The pixel gain value G can be obtained by dividing the amount of light at non-dimming by the amount of light at dimming, and performing a 1 / γ multiplier operation on the result. have.

This local dimming control method analyzes the data of the compensated one frame by bitmap method, calculates the degree of gray level aggregation, and generates a predicted value for the degree of gray level aggregation (S117) In the bitmap method, k (number of pixels) × k (number of pixels) (k is a positive integer) Subsequently scanning the compensation data for one frame while moving the analysis mask of one pixel interval left and right or up and down, replacing the pixel data of maximum gradation with "1". Then, the other gray level pixel data is replaced with "0". This local dimming control method counts the number of " 1 " to increase the predicted value of the degree of gradation when the count value is large, and decreases the predicted value of the degree of gradation aggregation when the count value is small. Here, the degree of gray level aggregation is larger when the predicted value is higher than when the predicted value is low.

In this local dimming control method, if the predicted value is larger than a predetermined target value (S118), the dimming curve is up-modulated to increase the dimming value (DIM) for each block (S119), and the result is fed back to S114 to repeat the processes S114 to S118. To perform. If the predicted value is smaller than the predetermined target value (S120), the dimming curve is down-modulated to decrease the dimming value (DIM) for each block (S21), and the result is fed back to S114 to perform the processes S114 to S120 again. This local dimming control method corrects the pixel gain value (G) through the above feedback process and converges the predicted value to the target value. The target value may be selected as an appropriate value to reduce the level of gradation while having a power consumption reduction effect.

This local dimming control method compensates the input data RGB with the pixel gain value G corrected so that the predicted value is equal to the target value, and outputs the final modulated data R'G'B '. The dimming value for each block adjusted to be equal to is output as the final dimming value (S122).

As described above, the liquid crystal display and the local dimming control method according to the present invention automatically adjust the pixel gain value by adjusting the amount of light at the time of non-dimming or the dimming value for each block according to the degree of gradation when local dimming is implemented. By correcting, the image quality can be greatly improved.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

1 is a view showing a liquid crystal display device according to an embodiment of the present invention.

2 illustrates an example of a local dimming control circuit.

3 is a diagram illustrating an example in which a surface light source is divided into blocks to implement local dimming.

4 is a diagram showing an analysis region of P (block number) × P (block number) size surrounding a block including a corresponding pixel.

5 shows another example of a local dimming control circuit.

FIG. 6 is a diagram illustrating an example of adjusting dimming value of each block by modulating a dimming curve. FIG.

7 is a view showing an example in which the gradation bunch is improved when the present invention is applied.

8 is a diagram illustrating an example of a local dimming control method.

9 is a view showing another example of a local dimming control method.

Description of the Related Art

10: liquid crystal display panel 11: timing controller

12: data driving circuit 13: gate driving circuit

14: local dimming control circuit 15: light source driving circuit

16: backlight unit 141, 241: image analysis unit

142,242: dimming value determining unit 143,243: light amount deriving unit

144,244: gain calculator 145,245: data modulator

146,246: bitmap analysis unit 147: light amount control unit

247: dimming value adjusting unit 148,248: gain value adjusting unit

Claims (12)

  1. A liquid crystal display panel;
    A backlight unit including a plurality of light sources for irradiating light to a rear surface of the liquid crystal display panel;
    A backlight driving circuit for driving the light sources in predetermined block units based on the dimming value for each block; And
    Compute a pixel gain value for compensating for the luminance deterioration due to the dimming value of each block, and adjust the first light amount indicating the amount of light reaching each pixel when all of the light sources are turned on at a constant brightness to adjust the gray level of each block. A local dimming control circuit for correcting the pixel gain value according to the degree of aggregation;
    The local dimming control circuit,
    An image analyzer for analyzing input data in units of blocks to derive a representative value for each block;
    A dimming value determiner which determines the dimming value for each block by mapping the representative value for each block to a preset dimming curve;
    A light amount deriving unit for deriving the first light amount and deriving a second light amount indicating the amount of light reaching the respective pixels at the time of local dimming as the dimming value for each block;
    A gain value calculator configured to calculate the pixel gain value for each pixel based on the first and second light amounts;
    A data modulator for compensating the input data by multiplying the input data by the pixel gain value; And
    And a gain value correcting unit configured to analyze the compensated input data to generate a predicted value for the degree of gray scale, and to adjust the first light amount according to the predicted value and feed it back to the gain value calculating unit. .
  2. delete
  3. delete
  4. The method of claim 1,
    The gain value correcting unit reduces the first light amount when the predicted value is larger than a predetermined target value, and conversely increases the first light amount when the predicted value is smaller than the target value, thereby converging the predicted value to the target value. LCD display device.
  5. A liquid crystal display panel;
    A backlight unit including a plurality of light sources for irradiating light to a rear surface of the liquid crystal display panel;
    A backlight driving circuit for driving the light sources in predetermined block units based on the dimming value for each block; And
    Comprising a local dimming control circuit for calculating a pixel gain value for compensating for the luminance degradation due to the dimming value for each block, and correcting the pixel gain value according to the degree of gradation of each block by adjusting the dimming value for each block; ;
    The local dimming control circuit,
    An image analyzer for analyzing input data in units of blocks to derive a representative value for each block;
    A dimming value determiner which determines the dimming value for each block by mapping the representative value for each block to a preset dimming curve;
    A first light amount indicating an amount of light reaching each pixel when all the light sources are turned on at a constant brightness, and a second light amount indicating the amount of light reaching each pixel at local dimming by the dimming value for each block; Light quantity derivation unit;
    A gain value calculator configured to calculate the pixel gain value for each pixel based on the first and second light amounts;
    A data modulator for compensating the input data by multiplying the input data by the pixel gain value; And
    And a gain value correcting unit configured to analyze the compensated input data to generate a predicted value for the degree of gradation, and to adjust the dimming value for each block according to the predicted value and to feed it back to the light amount deriving unit. .
  6. delete
  7. 6. The method of claim 5,
    The gain value corrector increases the dimming value for each block by upwardly modulating the dimming curve when the predicted value is larger than a predetermined target value. On the contrary, when the predicted value is smaller than the target value, the gain value correcting unit modulates the dimming curve downward when the prediction value is smaller than the target value. And reduce the convergence to converge the predicted value to the target value.
  8. In the local dimming control method of the liquid crystal display device including a liquid crystal display panel and a light source for irradiating light on the back of the liquid crystal display panel,
    Driving the light sources in predetermined block units based on a block-specific dimming value (A); And
    Calculating (B) a pixel gain value for compensating for a decrease in luminance due to the dimming value for each block, and correcting the pixel gain value according to the degree of gradation of each block;
    Step (B) is,
    Analyzing input data in the block unit to derive a representative value for each block (B1);
    Determining a dimming value for each block by mapping the representative value for each block to a preset dimming curve (B2);
    A first light amount indicating an amount of light reaching each pixel when all the light sources are turned on at a constant brightness, and a second light amount indicating the amount of light reaching each pixel at local dimming by the dimming value for each block; (B3);
    Calculating (B4) the pixel gain value for each pixel based on the first and second light amounts;
    Compensating for the input data by multiplying the input data by the pixel gain value (B5); And
    Analyzing the compensated input data to generate a predicted value for the degree of gradation, and adjusting the first amount of light according to the predicted value and feeding it back to the step (B4) (B6). Local dimming control method of display device.
  9. delete
  10. 9. The method of claim 8,
    In the step (B6), if the predicted value is larger than a predetermined target value, the first light quantity is decreased; conversely, if the predicted value is smaller than the target value, the first light quantity is increased to converge the predicted value to the target value. Local dimming control method of the liquid crystal display device.
  11. In the local dimming control method of the liquid crystal display device including a liquid crystal display panel and a light source for irradiating light on the back of the liquid crystal display panel,
    Driving the light sources in predetermined block units based on a block-specific dimming value (A); And
    Calculating (B) a pixel gain value for compensating for a decrease in luminance due to the dimming value for each block, and correcting the pixel gain value according to the degree of gradation of each block;
    Step (B) is,
    Analyzing input data in units of blocks to derive a representative value for each block (B1);
    Determining a dimming value for each block by mapping the representative value for each block to a preset dimming curve (B2);
    A first light amount indicating an amount of light reaching each pixel when all the light sources are turned on at a constant brightness, and a second light amount indicating the amount of light reaching each pixel at local dimming by the dimming value for each block; (B3);
    Calculating (B4) the pixel gain value for each pixel based on the first and second light amounts;
    Compensating for the input data by multiplying the input data by the pixel gain value (B5); And
    And analyzing the compensated input data to generate a predicted value for the gradation level, and adjusting the dimming value for each block according to the predicted value and feeding it back to the step B3 (B6). Local dimming control method of liquid crystal display device.
  12. The method of claim 11,
    In the step B6, when the prediction value is larger than a predetermined target value, the dimming curve is up-modulated to increase the dimming value for each block. On the contrary, when the prediction value is smaller than the target value, the dimming curve is down-modulated. And dimming value to converge the predicted value to the target value.
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